For reference: The equations will be ordered top to bottom 1-2-3 in my discussion.
We want to make the given equations with their given enthalpic values add up to the full reaction.
-Flip equation 1, resulting in a ΔH=103.8KJ
-Equation 2 multiplied by 3 to eliminate the Carbons
-Equation 3 multiplied by 4 to eliminate Hydrogen and add to the Oxygen
Use the numbers that you multiplied the equation by and add up:
103.8+3(-393.3)+4(-241.8)=-2043.3 KJ
